The invention relates to a process for preparing long-chain glycine-N,N-diacetic acid derivatives.
Glycine-N,N-diacetic acid derivatives can be employed as biodegradable complexing agents for alkali metal and heavy metal ions.
Various processes for preparing these compounds are known.
WO 94/29421 describes processes for preparing glycine-N,N-diacetic acid derivatives. These entail converting long-chain aliphatic aldehydes with iminodiacetonitrile and HCN alkylglycinonitrile-N,N-diacetonitrile, the resulting compound being hydrolyzed. The compounds can likewise be obtained by reacting the aldehydes with HCN and ammonia to give substituted amino nitrites, which are hydrolyzed to substituted amino acids, which is followed by reaction with formaldehyde and sodium cyanide. The process is too complicated for some compounds because long reaction times are necessary. Moreover the yields of the required compounds are still in need of improvement. The proposed processes are not always suitable for transfer to the industrial scale.
DE-A 195 18 986 describes a process for preparing glycine-N,N-diacetic acid derivatives by reacting glycine derivatives or their precursors with formaldehyde and hydrogen cyanide or reacting iminodiacetonitrile or iminodiacetic acid with appropriate aldehydes and hydrogen cyanide in aqueous acidic medium. The starting material employed in this case is the unpurified crude material derived from the industrial synthesis of glycine derivatives or their precursors or of iminodiacetonitrile or iminodiacetic acid, or mother liquors produced in syntheses of these types. The process is carried out as indicated in WO 94/29421.
DE-A-195 18 187 relates to a process for preparing glycine-N,N-diacetic acid derivatives by reacting glycine derivatives or their precursors with formaldehyde and alkali metal cyanide in aqueous alkali medium. The process is likewise based on the process described in WO 94/29421, but firstly from 0.5 to 30% of the amount of alkali metal cyanide required for the reaction is added to the glycine derivatives or their precursors, and then the remaining amount of alkali metal cyanide and the formaldehyde are metered in simultaneously over a period of from 0.5 to 12 hours. Even this variant of the process cannot eliminate all the abovementioned disadvantages.
It is an object of the present invention to provide a process for preparing glycine-N,N-diacetic acid derivatives by reacting iminodiacetonitrile with aldehydes and HCN or alkali metal cyanides, which avoids the abovementioned disadvantages and is suitable for transfer to the industrial scale. The process ought to give high yields in short reaction times; it is additionally intended to provide alternative processes which avoid the abovementioned disadvantages.
We have found that this object is achieved by processes with several variants as described below by means of component steps. The glycine-N,N-diacetic acid derivatives can be obtained, for example, by reactions shown in the two reaction schemes detailed below. 